1. Field of the Invention
The present invention relates to a memory, and more particularly, it relates to a memory comprising a refresh portion for reading and rewriting data from and in memory cells.
2. Description of the Background Art
In relation to a ferroelectric memory, a disturbance is generally known as such a phenomenon that data disappear due to reduction in the quantities of polarization of ferroelectric capacitors resulting from application of a prescribed voltage to memory cells connected to word lines other than a selected word line in a rewrite operation after a read operation and a write operation on the memory cells including the ferroelectric capacitors. A ferroelectric memory comprising a refresh portion for rewriting data in memory cells including ferroelectric capacitors and a counter for detecting access frequencies with respect to the memory cells in order to suppress such a disturbance is known in general, as disclosed in Japanese Patent Laying-Open No. 7-73682 (1995), for example.
When the access frequencies with respect to the memory cells detected by the counter reach a prescribed number of times, the conventional ferroelectric memory disclosed in the aforementioned Japanese Patent Laying-Open No. 7-73682 responsively forcibly rewrites data in the memory cells with the refresh portion, thereby suppressing a disturbance resulting from reduction in the quantities of polarization of the ferroelectric capacitors.
When the conventional ferroelectric memory disclosed in the aforementioned Japanese Patent Laying-Open No. 7-73682 is brought into a power-down state before the access frequencies with respect to the memory cells reach the prescribed number of times for the refresh operation, however, the data of the access frequencies detected by the counter may disappear before the ferroelectric memory performs the refresh operation. When the ferroelectric memory is repetitively subjected to a power-down operation before the access frequencies reach the prescribed number of times and a subsequent power-up operation in this case, disturbances resulting from access operations performed before the power-down operation are so accumulated in the memory cells that the data of the memory cells may disadvantageously disappear due to the accumulated disturbances.